Support design for tunnels with deep overburden in weak rock

Research output: Chapter in Book/Report/Conference proceedingConference contributionResearchpeer-review

Abstract

Tunnelling in weak rock under high stresses often results in damage to the lining and failure of bolts. Large displacements can lead to violation of the clearance profile, requiring costly, dangerous, and time-consuming repairs. The main problem is that conventional supports have a rather limited strain tolerance. Shotcrete, for example, can tolerate a maximum of 0.6% to 0.8% strain without failure. Any imposed strains beyond this level will lead to destruction of the lining and consequently a more or less complete loss of support resistance, causing additional displacements and disintegration of the rock mass. Over the last two decades, ductile elements have been developed and successfully used on a considerable number of tunnels. The aim of these elements is optimal utilization of the capacity of the lining, while preventing damage of the lining by limiting the resistance. Although this sounds simple, the task of designing such a ductile lining system is not at all trivial. Many factors need to be considered, like development of the displacements in relation to face advance and time. The ground structure and the relative orientation between the tunnel axis and dominant geological features, like foliation or bedding, strongly influence the longitudinal displacement profile. The development of the displacements over time also depends on the advance rate, influencing the degree of utilization of the shotcrete, which changes its properties over time. Currently used ductile element systems are presented and their characteristics as well as pros and cons discussed. More or less sophisticated tools for a preliminary design of ductile linings exist. Examples of applications are presented. Another issue is the performance of grouted rock bolts under large strains. Installation of bolts at the time of the largest strain rates in the rock mass close to the face results in considerable shear strains in the grout while it is setting. This may lead to a loss of bond between bolt and ground, making the bolts more or less ineffective. Special rib designs of the bolts can reduce this effect.

LanguageEnglish
Title of host publicationISRM AfriRock - Rock Mechanics for Africa
PublisherInternational Society for Rock Mechanics
Pages49-60
Number of pages12
Volume2017-October
ISBN (Electronic)9781920410995
StatusPublished - 1 Jan 2017
EventISRM AfriRock 2017 - Rock Mechanics for Africa - Cape Town, South Africa
Duration: 3 Oct 20175 Oct 2017

Conference

ConferenceISRM AfriRock 2017 - Rock Mechanics for Africa
CountrySouth Africa
CityCape Town
Period3/10/175/10/17

Fingerprint

weak rock
bolt
Bolts
Linings
overburden
Tunnels
tunnel
Rocks
shotcrete
rock
advance rate
damage
Disintegration
grout
geological feature
Shear strain
shear strain
foliation
strain rate
repair

Keywords

    ASJC Scopus subject areas

    • Geotechnical Engineering and Engineering Geology
    • Earth and Planetary Sciences(all)

    Fields of Expertise

    • Sustainable Systems

    Treatment code (Nähere Zuordnung)

    • Application

    Cite this

    Schubert, W. (2017). Support design for tunnels with deep overburden in weak rock. In ISRM AfriRock - Rock Mechanics for Africa (Vol. 2017-October, pp. 49-60). International Society for Rock Mechanics.

    Support design for tunnels with deep overburden in weak rock. / Schubert, W.

    ISRM AfriRock - Rock Mechanics for Africa. Vol. 2017-October International Society for Rock Mechanics, 2017. p. 49-60.

    Research output: Chapter in Book/Report/Conference proceedingConference contributionResearchpeer-review

    Schubert, W 2017, Support design for tunnels with deep overburden in weak rock. in ISRM AfriRock - Rock Mechanics for Africa. vol. 2017-October, International Society for Rock Mechanics, pp. 49-60, ISRM AfriRock 2017 - Rock Mechanics for Africa, Cape Town, South Africa, 3/10/17.
    Schubert W. Support design for tunnels with deep overburden in weak rock. In ISRM AfriRock - Rock Mechanics for Africa. Vol. 2017-October. International Society for Rock Mechanics. 2017. p. 49-60
    Schubert, W. / Support design for tunnels with deep overburden in weak rock. ISRM AfriRock - Rock Mechanics for Africa. Vol. 2017-October International Society for Rock Mechanics, 2017. pp. 49-60
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